1. Field of the Invention
This invention relates to methods and apparatus useful in the fluid treatment of surfaces. It has further utility in the minimization of fluid consumables by spreading of a treatment fluid into a thin film specific to a designated treatment zone. The invention has particular utility in connection with the fluid treatment of flat substrates and more specifically staining of biological tissue samples on glass slides and will be described in connection with such utility, although other utilities are contemplated.
2. Description of Related Art
The analysis of biological tissue samples is a valuable diagnostic tool used by the pathologist to diagnose many illnesses and by the medical researcher to obtain information about a cell structure.
In order to obtain information from a biological tissue sample it usually is necessary to perform a number of preliminary operations to prepare the sample for analysis. While there are many variations of the procedures to prepare tissue samples for testing, these variations may be considered refinements to adapt the process for individual tissues or because a particular technique is better suited to identify a specific chemical substance or enzyme within the tissue sample. However the basic preparation techniques essentially are the same. Biological tissue samples may derive from solid tissue such as from a tissue biopsy or may derive from liquid based preparations of cellular suspensions such as from a smear (e.g., PAP smear).
Typically such procedures may include the processing of the tissue by fixation, dehydration, infiltration and embedding; mounting of the tissue on a glass slide and then staining the sample; labeling of the tissue through the detection of various constituents; grid analysis of tissue sections, e.g., by an electron microscope, or the growing of sample cells in culture dishes.
Depending on the analysis or testing to be done, a sample may have to undergo a number of preliminary steps or treatments or procedures before it is ready to be analyzed for its informational content. Typically the procedures are complex and time consuming, involving several tightly sequenced steps often utilizing expensive and toxic materials.
For example, a typical tissue sample may undergo an optical microscopic examination so that the relationship of various cells to each other may be determined or abnormalities may be uncovered. Thus, the tissue sample must be an extremely thin strip of tissue so that light may be transmitted therethrough. The average thickness of the tissue sample or slice (often referred to as sections) is in the order of 2 to 10 micrometers (1 micrometer= 1/1000th of a millimeter). Typically, a tissue sample is either frozen or fixed in a material (a fixative) which not only preserves the cellular structure but also stops any further enzymic action which could result in the putrification or autolysis of the tissue.
After fixation, the tissue sample is then dehydrated by the removal of water from the sample through the use of increasing strengths of alcohol. The alcohol then is replaced by a chemical which mixes with wax or some other plastic substance impregnant which can permeate the tissue sample and give it a consistency suitable for the preparation of thin sections without disintegration or splitting.
A microtome is then utilized to cut thin slices from the tissue sample. The slices may be on the order of 5 to 6 micrometers thick while the diameter may be on the order of 5000 to 20000 microns long. The cut thin sections are floated on water to spread or flatten the section. The section is then disposed on a glass slide usually measuring about 8 by 2.5 centimeters (1×3 inches).
The wax or other impregnant is then removed by exposing the sample to a solvent, the solvent removed by alcohol, and the alcohol removed by decreasing the alcoholic concentrations until eventually the tissue is once more infiltrated by water. The infiltration of the sample by water permits the staining of the cell constituents by water soluble dyes.
Prior to the development of automated procedures for the preparation of tissue samples, it often took from two to ten days before the tissue could be examined under a microscope. In more recent years automated processes have been developed utilizing apparatus to transfer the sample from one fluid to another at defined intervals, and as a result the preparation time has been significantly reduced to 12 to 36 hours.
The foregoing discussion of the prior art derives largely from U.S. Pat. No. 5,675,715 to Bernstein et al. which describes an automated system for performing a plurality of independent analysis procedures simultaneously comprising a robotic arm which moves different tissue samples along a plurality of processing stations arranged along x and y coordinates wherein the tissue samples are subjected to various processes. See also U.S. Pat. No. 5,595,707 to Copeland et al., which describes an automated slide processing system comprising a reagent carousel cooperating with a sample support carousel to supply a sequence of preselected reagents to each of the samples with interposed mixing, incubating and rinsing steps cooperating therewith. Apparatus made in accordance with U.S. Pat. No. 5,675,715 and 5,595,707 and others is available commercially from Ventana Medical Systems, Inc. of Tucson, Ariz., and has achieved substantial commercial success and significantly reduced the time and cost of testing biological samples.
A biological tissue sample is finally viewed by a pathologist in an as-mounted state on a glass slide. Much of the processing of biological specimens, therefore, is adapted to the sequential application and removal of multiple fluids to an essentially two dimensional treatment zone on a 1″×3″ glass slide format.